Semiconductor device manufacturing: process – With measuring or testing
Reexamination Certificate
1996-09-16
2001-01-16
Mulpuri, Savitri (Department: 2812)
Semiconductor device manufacturing: process
With measuring or testing
C438S476000, C438S477000
Reexamination Certificate
active
06174740
ABSTRACT:
The present disclosure relates to subject matter contained in Japanese patent application No. 264743 (filed on Sep. 18, 1995) which is expressly incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for analyzing impurities contained within a silicon wafer in a simple manner with high accuracy and sensitivity.
2. Description of the Related Art
It is well known that, when there are present impurities such as metal elements (Al, Na, Fe, Cr, Ni, Cu, etc.) on or within a silicon wafer, these impurities have a harmful effect on electrical characteristics of a resultant semiconductor device. For this reason, it becomes essential to minimize or reduce the quantity of such impurities to a level as small as possible, which requires accurate analysis of the type, surface concentration and content of the impurities.
Conventional methods for directly analyzing metallic impurities on a silicon wafer or within a surface layer thereof include a secondary ion mass spectroscopy and a total reflection X-ray fluorescence analysis. In other matters, samples to be analyzed are taken from the surface layer of a silicon wafer. For example, a native oxide film on the surface layer of the silicon is dissolved with a vapor of hydrofluoric acid (HF), then a resultant dissolved solution is recovered as a sample, and then analyzed.
In both of these analysis methods, however, impurities present merely within the surface layer of the silicon wafer have been analyzed and it has been difficult to analyze impurities existing deep within the silicon wafer. Further, in the case where more impurities are contained deep within the wafer rather than the surface layer thereof or where the diffusion velosity of the impurities is fast, it has been impossible to attain its accurate quantitative evaluation.
Meanwhile, conventional methods for analyzing impurities in the bulk of a wafer include a method for analyzing a solution obtained by dissolving the entire wafer in a chemical agent solution and a secondary ion mass spectroscopy.
However, the former method has had a problem that not only a large quantity of the aforementioned solution is necessary with insufficient analysis accuracy and sensitivity but it also takes a lot of time to perform the analysis and the sample wafer is totally wasted. The latter method, on the other hand, has been disadvantageous in that expensive facilities are required and information obtained through a single sputtering analysis corresponds merely to that part of the sample which is as small as, e.g., 2 mm
2
(actually, a zone of 1 mm in diameter being able to be analyzed), which requires a lot of analysis time. In addition, the latter method is a destructive test.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method for analyzing impurities in the bulk of a silicon wafer which can analyze the impurities in the silicon wafer in a convenient and simple manner with high accuracy and high sensitivity and can suppress or minimize wastage and damage of a sample wafer, that is, the sample wafer being able to be used as an effective silicon wafer product.
In accordance with an aspect of the present invention, the above object is attained by providing a method of analyzing impurities in a bulk of a silicon wafer, which method comprises the steps of applying a mechanical damage onto one major surface of said silicon wafer to introduce distortions therein to form distorted layer, subjecting the silicon to a thermal oxidation process to form thermal oxide film on the wafer surface said distorted layer is formed thereon, dissolving the thermal oxide film or the thermal oxide film and surface layer of the wafer with a chemical solution or vapor to recover a dissolved solution, and analyzing the recovered solution.
In the invention, the step of subjecting the silicon wafer to the thermal oxidation process to form thermal oxide film on the wafer surface the distorted layer is formed thereon is carried out preferably by annealing the silicon wafer in the presence of an oxygen gas at a temperature of from 300° C. to 650° C. both inclusive for 2-120 minutes. Under these conditions, the formation of the thermal oxide film containing the distorted layer as well as the movement of the impurities within the silicon wafer into the distorted layer to be both promoted, thus allowing easy capture of the impurities. At temperatures less than 300° C., however, the movement velosity of the impurities within the silicon wafer becomes small, which requires a lot of time to realize sufficient capture of the impurities. At temperatures higher than 650° C., on the other hand, the diffusion velosity of the impurities within the silicon wafer becomes so fast that the diffusion energy is larger than the capture energy of the distorted layer, which makes it difficult to capture the impurities.
The reason why the time of the oxidation process is set in the aforementioned range is that a too short annealing time results in its insufficient capture effect and difficult evaluating of an absolute quantity of such impurities present within the wafer. A too long annealing time, on the other hand, results in reduction of its efficiency of the treatment and a fear of involving contamination from the outside even at the low temperature.
In accordance with another aspect of the present invention, there is provided a method of analyzing impurities in a bulk of a silicon wafer, which method comprises the steps of applying a mechanical damage onto one major surface of the silicon wafer to introduce distorted layer therein, converting the distorted layer at the surface of the wafer to a native oxide film (SiO
2
film) or a chemically-grown oxide film (SiO
2
film), subjecting the wafer to an annealing process at a temperature of from 300° C. to 650° C. both inclusive for 2-120 minutes, dissolving with a chemical solution or vapor any one selected from the group of (1) the native oxide film, (2) the native oxide film and the silicon surface layer directly therebelow, (3) the chemically-grown oxide film, and (4) the chemically-grown oxide film and the silicon surface layer directly therebelow to recover the dissolved solution, and analyzing the recovered solution.
In this connection, the above native oxide film is formed by a known method, for example, by keeping the silicon wafer in an atmosphere having a normal temperature and a normal pressure. The above “chemically-grown oxide film” can be formed, for example, by immersing a silicon wafer in a mixed solution of hydrogen peroxide, ammonia and water which is used at the time of cleaning the silicon wafer.
In this invention, when the silicon wafer is subjected to an annealing process at a temperature of from 300° C. to 650° C. both inclusive for 2-120 minutes, the impurities in the bulk of the silicon wafer are moved into either one or both of the distorted layer and oxide film.
In accordance with yet another aspect of the present invention, there is provided a method of analyzing impurities in a bulk of a silicon wafer, which method comprises the steps of applying a mechanical damage onto one major surface of the silicon wafer to introduce distortions therein to form distorted layer, subjecting the distorted layer at the surface of the silicon wafer to an atmospheric pressure chemical vapor deposition (CVD) process or a low pressure CVD process to deposit an oxide film (SiO
2
film) on the distorted layer, dissolving the oxide film or the oxide film and the surface layer of the wafer with a chemical solution or vapor to recover a dissolved solution, and analyzing the recovered solution.
In the present invention, the above step of depositing the oxide film is carried out preferably at a temperature of from 300° C. to 650° C. both inclusive for 2-120 minutes. At temperatures less than 300° C., the movement velosity of the impurities within the silicon wafer becomes small. At temperatures higher than 650° C., on the other hand, the diffusion velosity of the imp
Kosugi Akira
Nishijo Hirofumi
Ohta Yutaka
Mulpuri Savitri
Shin-Etsu Handotai & Co., Ltd.
Snider Ronald R.
Snider & Associates
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